The present invention relates to a vehicle lighting system including an additional illumination lamp for additionally illuminating ahead of a vehicle such as an automobile when the vehicle runs on a curved road.
In order to increase the driving safety of automobiles, there have been proposed adaptive front-lighting systems (AFS) which adopt a form in which the illumination ranges of headlamps of an automobile are directed in a direction in which the automobile is steered or a form in which the illumination ranges of the headlamps are expanded as the automobile is steered on a curved road. In the AFS, according to the former form in which the illumination ranges are swiveled towards the direction in which the automobile is steered, while there can be provided an advantage that a preferable range is illuminated in accordance with the steering of the automobile, a mechanism for swiveling the headlamps is necessary, resulting in a complicated construction. On the other hand, in the latter form in which auxiliary lamps are provided as additional illumination lamps to main headlamps (main lamps), so that the auxiliary lamps are illuminated when the automobile is steered so as to expand the illumination range in the direction in which the automobile is steered, when either the left additional illumination lamp 2L or the right additional illumination lamp 2R is illuminated, the illumination range of the left or right additional illumination lamp which is so illuminated can, as shown in FIGS. 2B, 2C, be added to the illumination range resulting solely from the illumination of either the main lamp 1L of the left headlamp LL or the main lamp 1R of the right headlamp LR, as shown in FIG. 2A, so that the illumination range in the direction in which the automobile is steered can be thus expanded. In this form, while there is an advantage that the necessary construction can be attained simply and inexpensively since no driving mechanism needs to be additionally provided for the headlamps, the expansion of the illumination range when the automobile is steered is determined only to an area extending along the direction of an optical axis of the additional illumination lamp 2L or 2R.
In the lighting system having the additional illumination lamps like this, since the optical axis of the additional illumination lamp is determined to be fixed, conventionally, a construction is adopted in which the additional illumination lamp is not lit up when the automobile is steered at a smaller steering angle than a predetermined steering angle which is preset in accordance with the optical axis angle of the additional illumination lamp (an angle formed by the straight forward traveling direction of the automobile and the optical axis of the additional illumination lamp) but is lit up when the automobile is steered at a steering angle equal to or larger than the predetermined steering angle so as to additionally illuminate the direction in which the automobile is steered. In this construction, however, when the automobile is steered at a steering angle close to the predetermined steering angle, there occurs a phenomenon where only with a slight change in the steering angle, the additional illumination lamp is repeatedly turned on and off (hereinafter, when referred to in this specification, this phenomenon is referred to as illumination hunting), and this troubles the driver of the automobile, which is not desired in consideration of safety driving.
To cope with the problematic illumination hunting, according to JP-A-2003-159986, as shown in FIG. 8A, a steering angle at which an additional illumination lamp is turned on as a result of the increase in steering angle (a turn-on reference steering angle θ12) and a steering angle at which the additional illumination lamp is turned off as a result of the decrease in steering angle (a turn-off reference steering angle θ11) are set to different steering angle positions so as to impart a hysteresis to the turn-on/turn-off control of the additional illumination lamp, whereby the frequent repetition of turn-on and turn-off of the additional illumination lamp is prevented even in the event that the automobile is steered at the predetermined steering angle. Namely, in FIG. 8A, when the steering angle represented by the axis of abscissas exceeds the turn-on reference steering angle θ12, the additional illumination lamp is turned on, and thereafter, when the steering angle is decreased to become smaller than the turn-off reference steering angle θ11, the additional illumination lamp is turned off. Thus, by setting the turn-off reference steering angle θ11 to the steering angle which is deviated in the straight forward traveling direction (a steering angle of 0 degree) from the turn-on reference steering angle θ12, even in the event that the steering angle changes within an angle range resulting from the deviation of the turn-off reference steering angle θ11 from the turn-on reference steering angle θ12, there occurs no case where the additional illumination lamp, which is illuminated, is turned off, the illumination hunting being thus prevented.
While the lamp of JP-A-2003-159986 is effective in preventing the occurrence of the illumination hunting in the additional illumination lamps, since the turn-off reference steering angle θ11 is set to the steering angle (to the steering angle of 0 degree in JP-A-2003-159986) which is situated apart by a large angle relative to the turn-on reference steering angle θ12, even in a situation in which the automobile approaches an end of a curved road and is then steered back to the straight forward traveling direction or steered in an opposite direction to cope with an oppositely directed curved road, the additional illumination lamp is not turned off, and thus, the direction which is different from the direction in which the automobile is now traveling is still illuminated, causing the driver to feel a feeling of physical disorder or drawing the line of sight of the driver to the different still illuminated direction, which is not preferable in consideration of safety driving. In particular, when the automobile is driven on the curved roads at low speeds, almost all the curves are curves of a small radius of curvature or corners such as at intersections, and in this case, since the steering wheel is steered at a large steering angle, it takes a certain time to steer it back to the straight forward traveling direction, and the driver is forced to feel a feeling of physical disorder during the time.
As to this point, as shown in FIG. 8B, while it may be considered possible to reduce the feeling of physical disorder that the driver has to feel by setting the turn-off reference steering angle θ11 to a steering angle position which is close to and is only slightly smaller than the turn-on reference steering angle θ12, in this case, it becomes difficult to set the turn-off reference steering angle θ11 appropriately. Namely, the setting of the turn-off reference steering angle θ11 at the steering angle position which is close to the turn-on reference steering angle θ12 is not good enough, since only with a change by a small steering angle in the steering angle, there is easily caused a situation in which the steering angle exceeds the turn-off reference steering angle θ11 or the turn-on reference steering angle θ12 in both the increasing and decreasing directions, and hence, the original object of ensuring the prevention of the occurrence of illumination hunting in the additional illumination lamps becomes difficult to be achieved. In addition, in JP-A-2003-159986, while the turn-on reference steering angle is changed in accordance with a change in vehicle speed of the automobile, it is difficult to solve the problem that the driver is forced to feel the feeling of physical disorder on the aforesaid occasions only with such a countermeasures.